Concrete finds extensive use as a building material due to its durability, strength, and ability to assume various shapes in its semi-fluid state before hardening. One serious and common problem encountered where concrete has been used is the cracking which occurs in the material over time due to such factors as freezing and thawing, ground settling, improper mix, improper application, and general deterioration with age. Similar problems are encountered with mortared joints between bricks, concrete blocks or stone, and with timber used in construction. Previously, these cracks have been repaired by removing areas surrounding the cracks, if possible, and filling the cracks with new concrete or mortar applied in the resulting cavity, usually using a trowel or similar instrument, at considerable expense if the repairs could be made at all. Another problem occurs where laminated construction methods are used for bridge decks, parking garages, and similar structures. Improper design and installation can result in delamination of the slab, which in turn causes extensive cracking, pot holes, and ultimate failure. Recently, epoxies and other polyester resins have been developed which not only adhere to the cracked material, filling voids and cavities and binding the surfaces together, but last almost indefinitely, ensuring that once a crack or cavity is properly filled, the problem at that particular area will cease to exist. Proper and prompt repair is important economically as well as structurally, since it will strengthen as well as prolong the life span of the repaired materials. Suitable dispensers have also been developed for metering, mixing and delivering these resins to the cracked surfaces at pressures in excess of 300 psi. However, many problems still exist in injecting the resins into the concrete, timber, or other material, since the techniques and tools used for the porting operation remain relatively undeveloped.
Regardless of the precise porting method selected, it is always necessary to first seal the crack or fault at the surface to contain the resin which is subsequently injected therein. This is normally accomplished by applying an epoxy paste or gel or a fast-setting cement mortar over the crack, usually with a spatula or putty knife. One of the most common methods of porting currently in use where the cracks are relatively free of impacted debris at the surface involves leaving a 1/4" wide gap in the paste used to seal the crack at the surface and setting a steel washer in this gap against the surface to be filled, held thereon by the paste. Following cure of the paste, a rigid 1/4" O.D. tube with a grommet on the end is manually held against the smooth seat provided by the washer while the resin is injected into the crack. A variation of this procedure involves setting an item such as a toothpick in the crack, which is then removed after the paste or gel is applied, leaving a hole through or against which a tube is placed and resin is injected.
This procedure requires that the tube be held in place using constant pressure while the fault is being filled, since any decrease in the holding pressure will result in leakage. However, the normally high-pressured injections used for these procedures are not easily contained by manually holding the tube against the surface to be injected. Where a relatively narrow crack is being filled, it may be necessary to apply pressure and hold the tube against the surface for ten minutes or more, due to the slow diffusion through the narrow fault, making the quality of the installation directly dependent upon the patience, strength, and stamina of the holder. Another method of porting commonly used where dirt and other contaminants have been driven into the fault at the surface involves drilling holes, approximately 1/2" in diameter, to a depth of approximately 1/2". These holes are drilled directly over the fault, normally using a waterflushed core or masonry bit or a hollow vacuumed bit to avoid impacting the removed material into the fault. A copper or plastic tube is then inserted into the hole and sealed with an adhesive gel or paste cone. The connection to the resin dispenser is made using a hose clamp, or by inserting a tapered plastic nozzle into the inserted tube and holding it therein for the duration of the injection process.
Once the injection of resin has been completed, the installation site is sealed, either by rubbing a paraffin block over the 1/4" area left uncovered in the first mentioned procedure, replacing the toothpick or similar item in the hole, or, where tubing has been used, by placing a plug or a cap on the tube to keep the injected resin in place. Where a fault is incorrectly or inadequately filled during the initial effort, it is normally impossible to re-inject the fault, since the previously injected and catalyzed resin prevents the injection of fresh adhesive. Thus, the anticipated repair strengths can not be realized and unsatisfactory results are obtained.